now, we expect there will be another strong show of force, but law enforcement officials say that there are no unexploded devices across the city. there were just those two planted bombs. people are still on edge, but it's not quite the police presence that we saw yesterday. >> all right, tahman bradley in boston, thank you. >> and, you know, tahman just briefly touched on the investigation into those bombings. >> yeah, of particular interest this morning is what's left of that common pressure cooker. that's where abc's brian ross continues our coverage. >> reporter: this is what remains of the pressure cooker turned into a homemade bomb seen in this fbi crime lab photo obtained by abc news. it was hidden in a black backpack. the simple bombs were responsible for 12 seconds of horror. cell phone footage shot by a spectator between the two explosions. authorities are going through race day videos frame by frame. here the white smoke seen after the detonation indicates a bomb built with low velocity explosive mixtures, not the more powerful military grade. >> they may not have had the res